1. Field of the Invention
The present invention relates to a thermocouple of an apparatus for manufacturing a semiconductor device, and more particularly, to a thermocouple in which one of the metal wires forming the thermocouple is coated with two different insulator materials, each of a predetermined length.
2. Description of the Related Art
Since the temperature during the process of manufacturing a semiconductor device is very high, a thermocouple is used for sensing the temperature instead of a general thermometer. The thermocouple has two metal wires, each composed of a different material. Only one end of each of the two metal wires is connected, thereby creating a potential difference between the two metal wires at the other (unconnected) end. This potential difference is then measured to thereby indirectly measure the temperature of the connected portion of the metal wires.
The principle utilized in the above thermocouple is the so-called Seebeck effect. The Seebeck effect is where a potential difference is generated due to the thermal driving force and is briefly described as follows.
In the case of a metal having a temperature gradient, electrons in the relatively hotter portion of the metal have an average kinetic energy higher than those in the relatively cooler portions thereof. This relationship can be represented by 3KT/2 where K is the Boltzmann's constant and T is absolute temperature. Accordingly, electrons have a tendency to move from the hotter region to the cooler region in order to reduce the average kinetic energy. That is, the electrons of the hotter region are diffused into the cooler region by a thermal driving force. However, when the electrons are thus diffused, a potential difference called the Seebeck voltage is created between the two regions, such that the cooler region electrons have a tendency to return to the hotter region. A state of equilibrium is realized when the Seebeck voltage is exactly balanced with the thermal driving force with respect to the electron flow. Therefore, the thermal driving force can be measured by the Seebeck voltage.
The Seebeck voltage differs according to the type of metal being employed in the thermocouple. When one end of each of two different metal wires is connected to each other and the connected portion is positioned where the temperature is to be measured, a potential difference is created between the unconnected ends as described above. Accordingly, the temperature of the portion to be measured can be indirectly measured by measuring the potential difference of the two metal wires. The above thermocouple adopts this principle.
FIG. 1 is a schematic view of a pyrogenic system generally used in a vapor oxidation process, showing an apparatus for manufacturing a semiconductor device using a thermocouple.
In detail, reference numeral 10 denotes a pyrogenic tube in which a pyrogenic reaction occurs, reference numeral 12 denotes a body of the pyrogenic system surrounding the pyrogenic tube 10, reference numerals 14 and 16 denote hydrogen and oxygen intakes for injecting hydrogen and oxygen, respectively, and reference numeral 18 denotes a heat collector mounted on the end (positioned inside the pyrogenic tube 10) of the hydrogen intake 14. Here, SiC having a high thermal conduction is, in general, used for the heat collector 18. Reference numeral 19 denotes a thermocouple having one end positioned near the heat collector 18 to measure the temperature of the heat collector and the other end connected to a temperature controller (not shown) positioned outside of the pyrogenic system. Reference numeral 30 denotes a lamp for supplying the heat collector 18 with thermal energy by irradiation. Here, since the lamp 30 should supply thermal energy in the form of light, an infrared lamp is generally used. Reference numeral 32 denotes a reflector for directing the heat generated from the lamp 30 onto the heat collector 18, and reference numeral 34 denotes a body of a heat generator for supporting the lamp 30 and the reflector 32.
The operation of the pyrogenic system will now be briefly described. Light energy generated from the lamp 30 collects on the heat collector 18, assisted by the reflector 32, and the temperature of the heat collector rises accordingly. Once the temperature of the heat collector 18 reaches a certain point, the hydrogen and oxygen injected through the intakes 14 and 16 are reacted to generate a vapor. The vapor flows into the pyrogenic tube 10, via a diffusion path (not shown) in which a wafer to be oxidized is located, to carry out a vapor oxidation process for forming an oxide film on the wafer.
For uniform vapor oxidation, the temperature of the heat collector 18 should rise to a predetermined temperature within a predetermined time. Then, to maintain this temperature, the temperature of the heat collector 18 is controlled by a temperature controller (not shown) which compares the heat collector temperature sensed by the thermocouple 19 to a predetermined value in order to control the power supplied to the lamp 30 and in turn the amount of light irradiated by the lamp 30. If, however, the temperature of the heat collector 18 is not rapidly transmitted to the thermocouple 19, the temperature of the pyrogenic tube 10 cannot reach the desired temperature in the proper time. Thus, the thermocouple material should exhibit high thermal conduction.
FIG. 2 is a schematic view of a conventional thermocouple. In detail, reference numerals 100 and 110 denote first and second metal wires having a connection point A where one end of each is connected. Reference numeral 120 denotes a base for supporting the first and second metal wires 100 and 110. The left part of the support 120 is positioned in the pyrogenic tube 10 of FIG. 1, and the right part is positioned at the outside of the pyrogenic tube 10 of FIG. 1. The right part has a portion that is connected to a temperature controller (not shown). Reference numeral 113 denotes an insulator for coating the second metal wire 110 between the connection point A and the support 120. Reference numeral 130 denotes a polymer (pliant) insulator for coating portions of the first and second metal wires 100 and 110 which are located between the support 120 and the temperature controller.
According to the conventional thermocouple as described above, quartz is used for the insulator 113 in order to obtain the desired high thermal conduction. Quartz, however, is highly brittle and is therefore subject to fracturing even with a slight physical shock, which may short-circuit the first and second metal wires 100 and 110. Accordingly, the life expectancy of the thermocouple is short, resulting in the frequent stoppage of the vapor oxidation process and subsequent productivity decreases.